Western blot of rat synaptic membrane showing specific immunolabeling of the ~102k GABAB R1 protein phosphorylated at Ser923 (control). The phosphospecificity of this labeling is shown in the second lane (lambda-phosphatase: Î»-Ptase). The blot is identical to the control except that it was incubated in Î»-Ptase (1200 units for 30 min) before being exposed to the phospho-Ser923 GABAB antibody. The immunolabeling is completely eliminated by treatment with Î»-Ptase.